The invention relates to a device comprising at least:
a rechargeable battery,
a measuring circuit for producing a magnitude that represents a state of charge of the battery based on at least two initial threshold voltages such as a set of values defined by two consecutive initial threshold values and associated to a magnitude representing a respective state of charge of the battery.
The invention also relates to a radiotelephone including such a device.
The invention relates to a method of estimating a state of charge of a battery.
The present invention is particularly interesting in applications linked with mobile telephony.
A rechargeable battery operates in successive cycles of use, a cycle corresponding to a complete charge followed by a complete discharge of the battery. When a battery becomes older, it deteriorates and, after various cycles of use, shows operating features which are different from those of a new battery. A battery comprises electrodes or plates, which are oxidized during operation and modify the operation features of the battery. A charge estimation device of a battery is known from document U.S. Pat. No. 5,404,106. This document proposes a device, which permits to estimate a rest charge capacity independently of the state of degradation of positive and negative plates of the battery. The device includes a table memory indicating the rest charge capacity as a function of a measurement of the internal resistance of the battery and a measurement of discharging current. A problem of the device described in this document is to indicate a rest charge capacity relative to the initial total charge capacity of the battery before a deterioration of the plates. Thus, for example, after various cycles of use of the battery, such a device does not necessarily indicate a maximum charge capacity when the battery is charged.
It is an object of the invention to provide a device that permits a precise and real estimation of the state of charge of a battery as a function of current operating features of the battery.
For this purpose, the measuring circuit of the device as described in the opening paragraph produces said magnitude based on corrected threshold values obtained from a correction of initial threshold values as a function of an approximation of the accumulated operating time of the battery.
A device according to the invention permits to effect a measurement of the state of charge of a battery while taking the modifications of the features of the battery due to a succession of various cycles of use of the battery into account. In contrast to the device described in the prior-art document, the state of charge is measured relative to the total charge capacity of the battery at the instant of the measurement; this total charge capacity being modified during the operation of the battery. An advantage of a device according to the invention is that a user of the battery charge capacity is correctly informed at a given instant about the total charge capacity at the same instant, whatever the state of aging of the battery.
In a preferred embodiment of the invention, the approximation of the accumulated operating time of the battery is a function of a measurement of the internal resistance of the battery.
In an embodiment of the invention, the measuring device comprises:
means for measuring the voltage on the terminals of the battery
means for comparing the voltage on the terminals of the battery with the corrected threshold values and for producing said magnitude that represents the state of charge of the battery as a function of the result of this comparison.
In a general manner, the rest charge capacity in a battery at a given instant may be estimated on the basis of a measurement of the voltage on the terminals of the battery. A set of threshold values of this voltage that correspond to various states of charge of the battery is available in a memory. The voltage measured on the terminals of the battery is compared with these threshold values and a magnitude representing the corrected state of charge of the battery is derived from this comparison.